1. Technical Field
The invention relates to pneumatic tires and more particularly to a run flat pneumatic vehicle tire containing a thin annular band which acts as a structural compression member when the tire is in the unpressurized or uninflated state which allows loads to act over a substantial portion of the circumference of the tire to enable the tire to run in the unpressurized condition. More particularly, the invention relates to such a band element which is circumferentially expandable to enhance the process of manufacturing the run flat tire without materially sacrificing the run flat capability achieved by the tire.
2. Background Information
Various tire constructions have been developed over the years which enable a tire to run in an uninflated condition, such as after receiving a puncture and loss of pressurized air, for extended periods of time and at relatively high speeds. This enables the vehicle operator to safely drive the vehicle to an appropriate location for repair or replacement of the uninflated tire. These tires are referred to as "run flat tires" and have been successful for certain applications and in certain types of tire constructions. One such type of run flat tire incorporates a thin annular high strength monolithic band which acts as a tension member when the tire is pressurized and acts as a structural compression member when the tire is in the unpressurized state, and are referred to as "banded run flat tires". Some examples of such banded run flat tires are shown in U.S. Pat. Nos. 4,428,411; 4,673,014; 4,794,966; 4,456,084; 4,111,249; 4,318,434; 4,459,167; 4,734,144 and5,879,484.
Nearly all of the band elements used in these prior art run flat tires are in-extensible in the circumferential direction when placed in the green tire prior to curing. The inability of the band to sufficiently expand during curing can cause problems of tread rubber porosity and air entrapment between the outside surface of the band and the adjacent surface of the tread rubber. To eliminate such air entrapment it requires extremely accurate control of the amount of tread rubber placed in the mold, which with many existing molds and control equipment is difficult to achieve to prevent or reduce such air entrapment. Thus, existing run flat pneumatic tires using the known nonextensible rigid bands are difficult to economically manufacture in order to eliminate the tread rubber porosity and air entrapment between the tread rubber and outer surface of the run flat band. Likewise, this inextensibility of the band may inhibit the intimate contact necessary between the band element and surrounding rubber to form the desired adhesive bond therebetween when using conventional curing systems and equipment.
U.S. Pat. Nos. 4,428,411; 4,673,014 and 4,794,966 disclose run flat tires which have an annular structural compression element in the inside surface of the crown portion of the tire wherein the compression element is a helix formed by closely spaced coils wound from a rod of various solid and tubular cross sections. The coils are in a stressed condition and are applied following the second stage expansion of the green tire and are difficult to form as a separate element and then inserted into the inner crown portion of the tire prior to molding. Likewise, the band elements of these three prior art patents are difficult to economically produce and be used in a conventional tire building process as is the expandable band of the present invention which requires only minor changes to the existing tire manufacturing process.
In summary, the present invention provides a band element for a run flat tire which is expandable during curing to reduce the problems of tread rubber porosity and air entrapment between the band and adjacent tread rubber to provide more intimate contact therebetween to form a better adhesion bond than possible and at reduced costs than achieved with the heretofore inexpandable band elements.